<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            box-sizing: border-box;
            width: 300px;
            height: 300px;
            display: flex;
            background-color: aqua;
            flex-direction: row-reverse;
            margin: 20px auto;
        }
        
        span {
            width: 100px;
            height: 100px;
            background-color: blue;
            border: 2px solid #ccc;
        }
    </style>
</head>

<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
    </div>
</body>

</html>